Automatic safety switch member

ABSTRACT

An automatic safety circuit for monitoring the power switching means controlling the main current circuit to an electric power load to automatically cut off the current in the event of a malfunction of the power switching means which causes it to continue to remain in its closed condition. The auxiliary switching circuit includes a switching arrangement for selectively disrupting the main current circuit, the switching arrangement being composed of a heatable switching element, an electrical resistance heating element formed as a coil which concentrically encloses the heatable switching element and an electrically insulating supporting sleeve which supports the coil and is disposed coaxial to the heatable switching element.

United States Patent [191 Hehl 1*Feb. 26, 1974 1 AUTOMATIC SAFETY SWITCHMEMBER [76] Inventor: Karl Hehl, Siedlung 183, D-7291 Lossburg, GermanyNotice: The portion of the term of this patent subsequent to Oct. 1,1989, has been disclaimed.

[22] Filed: July 19, 1972 [21] Appl. No.: 273,032

Related US. Application Data [63] Continuation-in-part of Ser. No.132,508, April 8,

1971, Pat. No. 3,697,812.

[30] Foreign Application Priority Data July 26, 1971 Germany 2137285[52] US. Cl. 219/501, 317/33 SC [51] Int. Cl. 1105b 1/02 [58] Field ofSearch 219/501, 469-471;

317/33 SC, 40 A, 40 R; 307/92, 94, 310; 337/182, 102, 103, 153; 338/252,270;

1,966,466 7/1934 Smalley 337/182 2,425,032 8/1947 Deyrup 338/270 UX3,383,496 5/1968 Ginsburg 219/501 3,581,062 5/1971 Aston 219/5013,616,533 11/1971 Heap et a1 174/52 PE 3,697,812 10/1972 Hehl 219/501Primary Examiner-B. A. Gilheany Assistant Examiner-1 E. Bell Attorney,Agent, or FirmSpencer & Kaye {57] ABSTRACT 174 52 as a coil whichconcentrically encloses the heatable switching element and anelectrically insulating sup- 5 References Cited porting sleeve whichsupports the coil and is disposed UNITED STATES PATENTS coaxial to theheatable switching element.

1,279,020 9/1918 Schweitzer 337/182 8 Claims, 7 Drawing Figures Mp OPATENTEDFEBZBW Y 3,794,831 1 SHEU 1 UF 2 Fig. 7

PATENTEDFEBZBIBN I 3,794,811

SHEEI 2 0F 2 RELAY CROSS-REFERENCE TO RELATED APPLICATION Thisapplication is a continuation-in-part of applicants copending U.S.Patent Application Ser. No. 132,508, filed on Apr. 8th, 1971 now U.S.Pat. No. 3,697,812, issued on Oct. th, 1972.

BACKGROUND OF THE INVENTION The present invention relates to animprovement in the automatic safety switch disclosed in my abovementioned U.S. Patent Application.

The prior application relates to an automatic safety switch formonitoring the power switching member of an electric current load, suchas, for example, an electric heater, an electric motor, or the like, inorder to prevent damage which might occur from a malfunction of thepower switching member controlling the main current circuit duringcutoff. The safety switch contains a relay serving as an auxiliaryswitching member which is electrically or mechanically connected withthe power switching member, an electrical connection between the maincurrent line leading to the electric load and, in one embodiment, anopening contact of the relay, or in another embodiment, an openingcontact of the relay which is in turn connected to the power switchingmember, and a device which is electrically connected with the openingcontact and which includes at least one resistance heating element and aheatable switching element in thermal contact with the heating elementfor disconnectng the load from the main current circuit when a certaintemperature is exceeded.

In the prior application the heatable switching element is usuallyprovided in the form of a fuse body and is flanked by two diametricallydisposed resistance heating elements. With such a design it mayhappen,particularly upon the occurrence of malfunctions that the resistanceheating element comes into electrical contact with the switchingelement, so that the resistance circuit is connected to the main oroperating current circuit. Such a short-circuit generally results indestruction of the amplifier of the safety circuit and damage to thecircuit board on which the resisance heating element and the switchingelement are disposed. In order to overome this danger it has become thepractice to additionally insulate the switching element, i.e., the fusebody, with a coating layer of plastic. Such an additional insulation hasthe drawback, however, that the limit temperature at which electricalcutoff of the load occurs can no longer be reproduced as accurately aswhen no insulation is used.

SUMMARY OF THE INVENTION It is, therefore, an object of the presentinvention to improve the safety circuit discribed above in such a mannerthat a short-circuit of the heatable switching element is effectivelyeliminated and the predetermined limit temperature at which safetyswitch cutoff occurs can be accurately reproduced.

This as well as other objects are accomplished according to the presentinvention by forming the resistance heating element as a coil ofresistance wire which concentrically surrounds the switching element andby providing a supporting sleeve which is disposed coaxial with theswitching element.

Advisably the switching element is a radially symmetrical fuse bodyhaving at least a central cylindrical section. The body is fullyenclosed by the cylindrical inner wall of the supporting sleeve.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a longitudinalcross-sectional view of a resistance heating element according to thepresent invention.

FIG. 2 is a front view of the heating element of FIG. 1.

FIG. 3 is a longitudinal, partially cross-sectional view of theresistance heating element of FIG. I mounted on a circuit board incombination with terminal columns for a fuse body to be inserted withinthe heating element.

FIG. 4 is a front view of the mounted heating element of FIG. 3 withoutthe connecting columns.

FIG. 5 is a top plan view, partially in longitudinal section, of thearrangement according to FIGS. 3 and 4 and including a fuse bodyconnected to the terminal columns.

FIG. 6 is a schematic top plan layout of a safety circuit utilizing theelement according to the present invention and having an electronicpower switching member.

FIG. 7 is a schematic circuit diagram of the safety circuit of FIG. 6.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The circuit illustrated inFIGS. 6 and 7 will be first described to permit a better understandingof the purpose, and importance, of the improved switching arrangementaccording to the invention.

In the circuit, a load 9 is held at a predetermined rated temperature byan electronic temperature control device. The temperature regulatingdevice has a suitable amplifier 8 which moniters the rated temperatureat the heated load 9. The amplifier 8 controls an auxiliary relay 7which together with the amplifier 8 forms an amplifier current circuit.Depending on whether the rated temperature at the heated load 9 has beenexceeded or not, the relay 7 with the aid of its switch contact 12switches a power switching member 6 on or off. The power switchingmember 6 controls a main current circuit 11 which is provided with asuitable fuse 1. The power switching member 6 may be an electronic powerswitching member, such as a thyristor. The power switching member 6which is controlled by the relay 7 via a suitable resistor 5, isdisposed directly in the main current circuit 11.

One significant component of the safety circuit is an electricalconnection 14 which is situated between the main current circuit 11 andthe opening contact 12 of the relay 7. Another significant component isa device 2, 3, 21, 29, 25, 90, which is disposed in the main currentcircuit 1 l and is electrically connected with the opening contact 12 ofthe relay 7 via a line 15. The device includes a resistance heatingelement 3, 21 and a heatable switching element or radially symmetricalfuse body 2 which is in thermal contact with the resistance heatingelement 3, 21 and which operates, for example, on a chemical basis tobecome nonconductive upon being heated to a certain temperature.

As can be seen in FIGS, 1-5, the resistance heating element 3, 21 isformed by an electrically insulating 18" extending outwardly from thecylindrical section, V

and operates on a chemical basis as a fuse body. The fuse body isenclosed by the cylindrical inner wall of the supporting sleeve 21. Thesleeve is formed preferably of a ceramic body and is disposed coaxiallyto the radially symmetrical switching element 2. The supporting sleeve21 is provided with a recess in its outer surface. The coil 3 is formedby a single winding and is disposed in the recess in the supportingsleeve.

A ceramic protective sleeve 29 is connected with a printed circuit typecircuit board 27 by means of slide fittings 25. The circuit board 27carries part of the current circuit of the resistance heating element 3,21 as well as of the main or operating current circuit 11. Theprotective sleeve 2? concentrically mounts the assembled switchingelement 2 and the supporting sleeve 21 'via the fittings 25 to thecircuit board 27. The fittings 25 are secured to the circuit board 27.The fittings 25 are secured to the circuit board 27 by rivet-likeportions including a stem 25' and a head 26.

Axial grooves are formed in the supporting sleeve 21. The input section3 and the output section 3", respectively, of the coil 3 pass throughthe grooves 20 and are electrically and mechanically connected with thecircuit board 27 by means of the fittings 25.

A pair of terminal columns 90 and 100 are mounted to the circuit board27 in a manner similar to the fittings 25. The one terminal 100 isdisposed in a plane A-A, which intersects the axis of the fuse body 2.The other terminal 90 is disposed outside of this plane in order tofacilitate mounting or dismounting of the fuse body in the supportingsleeve 21. The terminals 18, 18" are received within the columns 100,90, respectively, and are retained therein by clamping connections 111,112 in each column. As a result of the mounting of the terminals 18', 18to the columns 100, 90, the fuse body 2 is electrically connected to thecircuit board 27.

Referring again to FIG. 7, if the power switching member 6 becomesconductive due to a defect, for example, and the auxiliary relay 7remains disconnected, as shown in FIG. 7, one phase, Mp, of the maincurrent circuit 11 is connected to the resistance heating element 3, 21via the line 14, the opening contact 12, of the relay 7 and the line 15.The resistance heating element 3, 21 heats the switching element 2 untilit exceeds a predetermined limit temperature. As a result, the maincurrent circuit 11 is cut off and thus the current flow for the electricload 9 is interrupted. The placement of the resistance heating wire 3concentric with the fuse body 2 offers absolute protection against ashort circuit. Furthermore the fuse body 2 no longer needs to besoldered.

The fuse body 2 is constituted by a thermolabile substance disposed inthe conductive path. The fuse body is well-known and can be obtained onthe market.

It will be understood that the above description of the presentinvention is susceptible to various modfications, changes, andadaptations, and the same are intended to be comprehended within themeaning and range of equivalents of the appended claims.

I claim:

.1. A circuit arrangementfor supplying current to an electric powerload, as for example, an electric heater, an electric motor and thelike, said circuit arrangement comprising, in combination:

a main current circuit having said load and a power switching means forcontrolling the current to said.

load connected in series;

a first means for'controlling the opening and closing of said powerswitching means; and

an automatic safety circuit means for monitoring said power switchingmeans controlling said main current circuit to prevent damage to saidload which might occur as a result of a malfunction of said powerswitching member causing it to remain closed when the main current tothe load is to be cut off said automatic safety circuit means includrent to said load out off, to cause said second means to disrupt saidmain current circuit in the event said power switching means has notopened, said second means including a heatable switching element, anelectrical resistance heating element formed as a coil which enclosessaid heatable switching element, and an electrically insulatingsupporting sleeve which supports said coil and is disposed around saidheatable switching element.

2. The circuit arrangement as defined'in claim 1, wherein saidsupporting sleeve is formed as a ceramic body having a cylindrical innerwall, and said heatable switching element is a radially symmetrical fusebody having at least a central cylindrical section, the fuse body beingenclosed by said cylindrical inner wall.

3. The circuit arrangement as defined in claim 1,

wherein said supporting sleeve has an outer surface with a recesstherein, and said coil is formed by a single winding and is disposed insaid recess.

4. The circuit arrangement as defined in claim 1, further comprising acircuit board carrying a printed circuit, a protective sleeve whichencloses said supporting sleeve, and means for fitting said protectivesleeve to said circuit board, said circuit board being a component ofthe current circuit of said resistance heatingelement and the maincurrent circuit.

5. The circuit arrangement as defined in claim 4, further comprisingterminal columns and means for connecting said columns to said circuitboard so that said columns serve as electrical conductors, and clampingmeans, wherein said heatable switching element is a radially symmetricalfuse body having a central cylindrical section and a pair of terminalswhich are connected to a respective terminal column by said clampingmeans, said terminals being disposed, when connected to a respectiveterminal column, in a plane which intersects the axis of the fuse body.

6 6. The circuit arrangement as defined in claim 4, output portion,respectively, of said coil. wherein said coil has an input and outputportion, and 8. The circuit arrangement as defined in claim 1, saidsupporting sleeve has axial grooves therein which wherein said switchingelement is of a material whose receive said input and output portion,respectively. electrical characteristics charge when said element is 7.The circuit arrangement as defined in claim 6, 5 heated beyond apredetermined temperature so as to wherein said fitting means enclosesaid protective cause the main current circuit to open. sleeve andinclude means for receiving said input and l UNITED STATES PATENT OFFICECERTIFICATE v()F CORRECTION Karl Hehl Inventor(s) It is certified thaterror appears in the above-identified patent and that said LettersPatent are hereby corrected as shown below:

Column 6, line 4, "charge" should read change Signed and sealed this28th day of January 1975.

(SEAL) Attest:

MCCOY M. GIBSON JR. c. MARSHALL DANN Attesting Officer Commissioner ofPatents USCOMM-DC 60376-P69 u.s. GOVERNMENT PRINTING OFFICE: 930

FORM PO-\ 050 (10-69) UNITED STATES PATENT OFFICE CERTIFICATE OFCORRECTION Patent 3-794.8ll Dated Februarv 26th, 1974 Inventor(s) KarlHehl It is certified the 1t error appears in the above-identified patentand that said Letters Patent are hereby corrected as shown below:

In the heading of the patent, line 5, change "Oct. 1'' to -October lO-..Column 3, lines 64 and 65, change "modifications" to -modifi cations-.Column 4, line l7, after "off" insert a comma Signed and sealed this17th day of September 1974.

(SEAL) Attest:

McCOY M. GIBSON JR. C. MARSHALL DANN At'testing Officer CommissionerofPatents FORM PO 105 (10.69) 'USCOMM'DC 60376-P69 UIS. GOVERNMENTPRINTING OFFICE: IQD 0-366-334,

UNITED STATES PATENT OFFICE Karl Hehl Patent No.

Inventor(s) It is certified that error appears in the above-identifiedpatent and that said Letters Patent are hereby corrected as shown below:

Column 6, line 4, "charge" should read change Signed and sealed this28th day of January 1975 (SEAL) Attest:

MCCOY M. GIBSON JR. Attesting Officer C. MARSHALL DANN Commissioner ofPatents USCOMM-DC 003764 69 FORM PC4050 (10-69) u.s. covzaunzn'r rnlmrmsOFFICE: 930

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent 3 .794 .811Dated Februarv 26th, 1974 InVentofls) rl Hehl It is certified that errorappears in the above-identified patent and that said Letters Patent arehereby corrected as shown below:

In the heading of the patent, line 5, change "Oct. 1" to --Octoberl0--.I Column 3, lines 64 and 65, change "modfications" toi--modifications--.Column 4, line l-7, after "off" insert a comma Signed and sealed this17th day of September 1974.

(SEAL) Attest:

McCOY M. GIBSON JR. c. MARSHALL DANN Attesting Officer Commissioner ofPatents 'USCOMM-DC 60375-P69 F ORM PO- I 050 10-69) U.S4 GOVERNMENTPRINTING OFFICE: I989 0-36S33l.

1. A circuit arrangement for supplying current to an electric powerload, as for example, an electric heater, an electric motor and thelike, said circuit arrangement comprising, in combination: a maincurrent circuit having said load and a power switching means forcontrolling the current to said load connected in series; a first meansfor controlling the opening and closing of said power switching means;and an automatic safety circuit means for monitoring said powerswitching means controlling said main current circuit to prevent damageto said load which might occur as a result of a malfunction of saidpower switching member causiNg it to remain closed when the main currentto the load is to be cut off said automatic safety circuit meansincluding: second means for disrupting said main current circuit whensaid second means is subjected to a control current therein andauxiliary switch means, controlled by said first means and connectedbetween said second means and a point of said main current circuitlocated between said load and said power switching means, for connectingsaid second means to said point so as to establish a control currentpath to said second means when said main current circuit is to bedisrupted via said power switching means and the main current to saidload cut off, to cause said second means to disrupt said main currentcircuit in the event said power switching means has not opened, saidsecond means including a heatable switching element, an electricalresistance heating element formed as a coil which encloses said heatableswitching element, and an electrically insulating supporting sleevewhich supports said coil and is disposed around said heatable switchingelement.
 2. The circuit arrangement as defined in claim 1, wherein saidsupporting sleeve is formed as a ceramic body having a cylindrical innerwall, and said heatable switching element is a radially symmetrical fusebody having at least a central cylindrical section, the fuse body beingenclosed by said cylindrical inner wall.
 3. The circuit arrangement asdefined in claim 1, wherein said supporting sleeve has an outer surfacewith a recess therein, and said coil is formed by a single winding andis disposed in said recess.
 4. The circuit arrangement as defined inclaim 1, further comprising a circuit board carrying a printed circuit,a protective sleeve which encloses said supporting sleeve, and means forfitting said protective sleeve to said circuit board, said circuit boardbeing a component of the current circuit of said resistance heatingelement and the main current circuit.
 5. The circuit arrangement asdefined in claim 4, further comprising terminal columns and means forconnecting said columns to said circuit board so that said columns serveas electrical conductors, and clamping means, wherein said heatableswitching element is a radially symmetrical fuse body having a centralcylindrical section and a pair of terminals which are connected to arespective terminal column by said clamping means, said terminals beingdisposed, when connected to a respective terminal column, in a planewhich intersects the axis of the fuse body.
 6. The circuit arrangementas defined in claim 4, wherein said coil has an input and outputportion, and said supporting sleeve has axial grooves therein whichreceive said input and output portion, respectively.
 7. The circuitarrangement as defined in claim 6, wherein said fitting means enclosesaid protective sleeve and include means for receiving said input andoutput portion, respectively, of said coil.
 8. The circuit arrangementas defined in claim 1, wherein said switching element is of a materialwhose electrical characteristics charge when said element is heatedbeyond a predetermined temperature so as to cause the main currentcircuit to open.